\begin{tikzpicture}[>=Stealth, scale=0.8]
    \draw [->] (-1, 0) -- (4, 0) node[anchor=west] {$x$};
    \draw [->] (0, -1) -- (0, 4) node[anchor=east] {$y$};
    \node at (-0.3, -0.3) {$O$};

    \coordinate (O) at (0, 0);
    \coordinate [label=0:$Z_1$] (Z1) at (3, 1);
    \coordinate [label=90:$Z_2$] (Z2) at (1, 2);
    \draw[->, thick] (O) -- (Z1);
    \draw[->, thick] (O) -- (Z2);
    \draw[->, thick] (Z1) -- (Z2);
\end{tikzpicture}
